As computing devices have increased in capabilities and features, demand for data storage devices has grown. Data storage devices have been used, for example, to store program instructions (i.e., code) that may be executed by processors. Data storage devices have also been used to store other types of data, including audio, image, and/or text information, for example. Recently, systems with data storage devices capable of storing substantial data content (e.g., songs, music videos, etc. . . . ) have become widely available in portable devices.
Such portable devices include data storage devices that have small form factors and are capable of operating from portable power sources, such as batteries. Some data storage devices in portable devices may provide non-volatile memory that is capable of retaining data when disconnected from the power source. Portable devices have used various non-volatile data storage devices, such as hard disc drives, EEPROM (electrically erasable programmable read only memory), and flash memory.
Flash memory has become a widely used type of semiconductor memory. Flash memory may provide a non-volatile memory in portable electronic devices and consumer applications, for example.
Two types of flash memory are NOR flash and NAND flash. In general, NOR flash may differ from NAND flash in certain respects. For example, NOR flash typically provides the capacity to execute code in place, and is randomly accessible (i.e., like a RAM). For example, NOR flash may provide code storage and direct execution in portable electronics devices, cell phones, and PDAs.
In comparison, NAND flash can typically erase data more quickly, access data in bursts (e.g., 512 byte chunks), and may provide more lifetime erase cycles than comparable NOR flash. NAND flash may generally provide non-volatile storage at a low cost per bit as a high-density file storage medium for consumer devices, such as digital cameras and MP3 players, for example. NAND flash may also be used for applications such as data storage in camera cell phones.
In some flash memory manufacturing environments, a small percentage of flash memory dies may have defects that may be detected by testing. One example of a defect is a bit error at a particular memory location. Some defects may be compensated for by techniques such as redirecting read/write accesses from defective memory locations to a set of redundant memory locations.
In some cases, more than one die of flash memory may be assembled together into a single integrated circuit (IC) package. In such multi-die flash memory packages, tests may be performed to detect defects in any of the flash memory dies in the package. The entire package may be discarded if any individual flash memory die in the package has more than an acceptable number of defects.